PB with Different size of painting materials in Landscape + seams

Hello,
I have a problem with my Landscape. I have two difference size of the same painting material in my Landscape. ( in picture : A and B have different size but have there are same material …How can I resize this part ?

And I have a second problem, I have transparent line ( red arrow ). How fix it ?

Thanks you for your help !

Have a nice day.